Preform for plastics material bottles or wide-necked vessels

ABSTRACT

A preform for manufacturing plastics material bottles or wide-necked vessels is described, having a rigid, substantially elongate, frustoconical body portion that is closed at one of its longitudinal ends by a dome-shaped end portion and at its opposite longitudinal end adjoins via a preform collar a neck portion provided with a pouring opening. The preform possesses in the body portion an external diameter that is reduced from the preform collar to the end portion. The body portion has a wall thickness which changes over its longitudinal extension substantially constantly by up to +2 mm. For this purpose, it possesses an internal diameter which decreases substantially constantly from a transition to the preform collar up to a transition to the dome-shaped end portion.

BACKGROUND

1. Field of the Invention

The invention relates generally to a preform for plastics material bottles or wide-necked vessels, and more specifically to a perform having a rigid, substantially elongate, frustoconical body portion that is closed at one of its longitudinal ends by a dome-shaped end portion and at its opposite longitudinal end adjoins, via a preform collar, a neck portion provided with a pouring opening and has an external diameter that is reduced from the preform collar to the end portion.

2. State of the Art

The previously conventional containers made of white or coloured sheet metal, of glass or else of ceramic are increasingly being superseded by containers made of plastics material. In particular for the packaging of pourable media, for example of cleaning utensils, body care products, cosmetics, motor vehicle media, etc., use is made mainly of plastics material containers. The low weight and the relatively low costs are no doubt key factors in this substitution. The use of recyclable plastics materials and the overall more advantageous total energy balance in the manufacture thereof also contribute to promoting consumers' acceptance of plastics material containers, in particular of plastics material bottles.

The most frequently used plastics material bottles are usually manufactured in what is known as an injection stretch blow moulding method. These methods are a combination of injection moulding and blow moulding. In this case, a preform is first manufactured in an injection mould in an injection moulding process. Recently, extrusion methods have also been proposed for manufacturing preforms. The preform has a substantially elongate body, one longitudinal end of which is closed off by a dome-shaped end portion. A neck portion comprising a pouring opening adjoins the other longitudinal end of the body. This neck portion conventionally already displays the subsequent shape of the bottleneck. Threaded portions or the like are usually also already formed on the outside of this neck portion for securing a closure part. The preform is removed, after manufacture thereof in a plastics material injection moulding method, from the injection mould, if necessary conditioned and introduced into a blowing mould of a blowing machine, in which it is finally inflated with excess pressure to the desired shape and is additionally stretched using a stretching mandrel. Also already known is an injection blow moulding method in which the blowing process follows on immediately from the injecting of the preform. The preform remains in this case on the injection mandrel and part of the injection mould forms a portion of the blowing mould.

For the manufacture of plastics material bottles or wide-necked vessels having a reinforced bottom region, specific preforms are known, having a stepped or tiered bottom portion. In these preforms, the wall thickness of the preform changes at the transition to the dome-like bottom portion in a stepwise manner and suddenly assumes a higher value. During the manufacture of preforms of this type by injection moulding, the sudden change in wall thickness can lead to problems. In particular, there can occur at the transition from the wall thickness of the body to the greater wall thickness of the bottom portion during the injection moulding method local temperature peaks which impair the properties of the plastics material. In the stretch blow moulding method too, changes in the wall thickness of the preform, which are staggered in a stepwise manner, can lead to problems which manifest themselves as non-uniformities in the fully stretch blow-moulded plastics material bottle. It is often also desirable to form the preform, at the particularly critical region of transition from the neck portion to the body, in what is known as the preform collar, with a greater wall thickness. This also leads, in the known preforms, to staggered changes in wall thickness which can lead to the above-described problems.

U.S. Pat. No. 4,044,086 discloses a preform, the wall thickness of which decreases substantially constantly over its longitudinal extension, and the internal diameter i of which decreases likewise substantially constantly from a transition to the preform collar up to a transition to the dome-shaped end portion. In the longitudinal extension, the wall thickness increases downwardly from 0.047 inch (1.2 mm) to 0.18 inch (4.7 mm). Thus, the change in wall thickness along the longitudinal extension of the preform is more than 2 mm.

EP 0 311 161 discloses a method and an apparatus for manufacturing multi-layer, thermoplastic preforms from which blow-moulded containers for food products and beverages can be made. The figures show a mould for manufacturing a frustoconical preform. The mould can be used to manufacture preforms which subsequently have on the neck portion a cylindrical portion which merges with the body portion via a conical portion of substantially the same wall thickness. The external diameter of the preform collar decreases from the neck portion up to the body portion.

The present invention therefore provides a preform for the manufacture of plastics material bottles or wide-necked vessels in an injection blow moulding or injection stretch blow moulding method. The preform eliminates problems during manufacture thereof in a plastics material injection moulding method and in the subsequent blow moulding method. In both, the required mechanical strengths and the thermal stability of the plastics material bottle produced from the preform or of the wide-necked vessel are ensured.

Thus, a preform for manufacturing plastics material bottles or wide-necked vessels is provided having a body portion that has a wall thickness that changes over its longitudinal extension substantially constantly by up to plus or minus 2 mm, and possesses an internal diameter which decreases substantially constantly from a transition to the preform collar up to a transition to the dome-shaped end portion. Further developments and/or advantageous various embodiments of the invention are set forth herein.

SUMMARY OF THE INVENTION

The invention provides a preform for manufacturing plastics material bottles or wide-necked vessels, having a rigid, substantially elongate, frustoconical body portion which is closed at one of its longitudinal ends by a dome-shaped end portion and at its opposite longitudinal end adjoins via a preform collar a neck portion provided with a pouring opening. The preform possesses in the body portion an external diameter which is reduced from the preform collar to the end portion. The body portion has a wall thickness which changes over its longitudinal extension substantially constantly by up to ±2 mm. For this purpose, it possesses an internal diameter which decreases substantially constantly from a transition to the preform collar up to a transition to the dome-shaped end portion.

The fact that sudden changes in wall thickness are avoided makes allowance for the problem of local exposure to heat during the injecting of the preform with plastics material. This also ensures that the preform has uniform wall thicknesses over its circumference. Shrinkage cavities or the like, as a consequence of turbulences of the plastics material, at edges and corners can thus reliably be avoided. During stretch blow moulding of the preform, the forces are distributed more uniformly. Local overstressing, which might lead to material weakening, or overheating at edges and corners are as a result avoided. As a consequence of the substantially constantly preceding changes in wall thickness of merely up to 2 mm in the body portion of the preform (either an increase in wall thickness or a decrease in wall thickness by at most 2 mm from the transition of the preform collar up to the transition to the dome-shaped end portion), the behaviour of the plastics material during stretch blow moulding is easier to predict and to control. As a result, plastics material bottles or wide-necked vessels having the desired properties can be manufactured more reliably. Irrespective of the change in the wall thickness of the body portion, the internal diameter of the body portion decreases substantially constantly over its longitudinal extension toward the dome-shaped end portion. Undercuts are avoided, so that simple removability of the injection core from the mould continues to be ensured.

A variant of the preform provides for the preform collar forming the transition from the neck portion to the body portion to have an external diameter which changes from the neck portion to the body portion. The preform collar forms, after the blow moulding method, the shoulder region of the manufactured plastics material bottle or the wide-necked vessel. As a result of the embodiment according to the invention, the subsequent shape of the generated container is taken into account already on the preform. As a result, the preform collar is stretched neither excessively nor too little during the blow moulding method and the subsequent shoulder region of the container obtains its optimum strength. In this case, provision may be made for the external diameter of the preform collar to increase in size from the neck portion to the body portion at least in the partial portion adjoining the body portion. This is particularly advantageous in plastics material containers having bulky bodies. Another variant of the preform provides, on the other hand, for the external diameter of the preform collar to decrease in size from the neck portion to the body portion at least in the partial portion adjoining the body portion. This variant embodiment of the preform is used particularly advantageously in the manufacture of wide-necked vessels. It will be understood that the increase or reduction in external diameter cannot take place immediately after the transport ring. There can also first be provided a substantially cylindrical portion which is adjoined by the region, the external diameter of which varies. The internal diameter of the preform collar decreases, on the other hand, substantially constantly from the neck portion to the body portion of the preform.

In order to prevent sudden transitions from the preform collar to the body portion, the outer wall and the inner wall of the preform collar enclose with the adjoining outer wall and inner wall of the body portion in each case obtuse angles. The angles are 130° to less than 180°, preferably between 158° and 178° and most particularly preferably between 160° and 175°.

If the body portion of the preform has a minimum wall thickness which does not drop below 0.8 mm, sufficient rigidity and stability of the plastics material container made from the preform are ensured. On the other hand, the maximum wall thickness of the body portion does not exceed 6 mm. This ensures sufficiently rapid softening of the preform as a whole and uniform stretching of the body portion during the blow moulding method.

For the uniformity of the process of manufacturing the preform by injection moulding, extrusion, but also by spray foaming, it has been found to be expedient if the body portion has an internal diameter and an external diameter which are each reduced from the preform collar to the dome-shaped end portion by 0.1 mm to at most 3.5 mm.

A sudden change in wall thickness is also avoided at the transition from the body portion to the end portion. For this purpose, the dome-shaped end portion has a wall thickness which is reduced from the wall thickness of the body portion up to an injection point by 0% to 50%, preferably 20 to 50%. The wall thickness in the injection point is in this case not taken into account. The wall thickness in the end portion is in this case selected in accordance with the type of bottom to be manufactured, in order to impart optimum rigidity and stability to the fully blow-moulded container.

The preform according to the invention can be made of the conventional materials used for the stretch blow moulding method, for example of PET. Advantageously, at least 85% of the body portion of the preform is made of materials selected from the group consisting of polyesters (including PET, PBT, PLA, and PEN), copolyesters, polyolefins (in particular PP, HDPE) and polystyrenes (GPS or HIPS).

The preform according to the invention is optimised inter alia for manufacture by injection moulding, extrusion or spray foaming.

Plastics material bottles and wide-necked vessels made from the preforms embodied in accordance with the invention are distinguished by high mechanical strengths and high thermal stability. For example, they allow the formation of a champagne bottom for the storage of highly carbonated beverages which can build up high pressure inside the bottle during storage or during transportation.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and features will emerge from the subsequent description of exemplary embodiments of the invention with reference to the schematic drawings, in which:

FIG. 1 is a non-true-to-scale, schematic axial section of a first exemplary embodiment of a preform according to the invention;

FIG. 2 is a non-true-to-scale, schematic axial section of a second exemplary embodiment of the preform;

FIG. 3 is a non-true-to-scale, schematic axial section of a third exemplary embodiment of the preform; and

FIG. 4 is a non-true-to-scale, schematic view of a fourth variant of the preform according to the invention.

For the sake of clarity, in the illustrations, like parts are denoted in all cases by the same reference numerals.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The preform illustrated in FIG. 1 is denoted in its entirety by reference numeral 1. It has a rigid, substantially elongate, frustoconically embodied body portion 2, one longitudinal end of which is closed by a dome-shaped end portion 3. The other longitudinal end of the body 2 is adjoined in the first place by what is known as a preform collar 8 which forms the transition of the body portion 2 to a neck portion 4 comprising a pouring opening 5. The neck portion 4 conventionally already displays the subsequent shape of the neck of the inflated plastics material bottle or a wide-necked vessel. Threaded portions 6 or the like are formed on the outside of the neck portion 4 for securing a closure part. The preform 1 is manufactured for example in an injection moulding method. Alternative manufacturing methods are for example extrusion or, with appropriate raw materials, spray foaming.

The preform collar 8 is separated from the neck portion 4 by an annularly encircling transport ring 7. The preform collar 8 has an axial length x which is measured on its inner wall 81 and corresponds, in the illustrated exemplary embodiment, roughly to an axial length l of the preform collar 8 on its outer wall 82. However, the two axial extensions of the inner wall 81 and the outer wall 82 of the preform collar 8 do not necessarily have to have the same length.

The body portion 2 of the preform 1 has an external diameter a, which substantially constantly decreases in size from the preform collar 8 up to the dome-shaped end portion 3. The internal diameter i of the body portion 1 also substantially constantly decreases in size from the preform collar 8 to the end portion 3. The body portion 2 possesses a wall thickness w which changes substantially constantly along the longitudinal extension of the body portion 2 from the preform collar 8 to the dome-shaped end portion 3. In the illustrated exemplary embodiment, the wall thickness w of the body portion 2 is reduced constantly by up to ±2 mm toward the end portion 3. In this case, the wall thickness w of the body portion 2 of the preform 1 does not drop below a minimum wall thickness of 0.8 mm.

A second exemplary embodiment of the preform is denoted in FIG. 2 in its entirety by reference numeral 11. It has, again, a body portion 2 which on the one hand adjoins a dome-shaped end portion 3 and on the other hand is connected to a neck portion 4 via a preform collar 8. The neck portion 4 and the preform collar 8 are separated from each other by a transport ring 7. Again, threaded portions or the like (not shown in greater detail) are formed on the neck portion 4 for securing a closure part. FIG. 2 shows that the preform 11 has in its preform collar 8 an external diameter d which increases in size substantially constantly over a substantial portion of its longitudinal extension from the transport ring 7 toward the body portion 2. The preform collar 8 has an internal diameter e which decreases in size toward the body portion 2. The transition of an outer wall 82 of the preform collar 8 to the outer wall 22 of the body portion 2 takes place at an obtuse angle β. The obtuse angle of transition β is preferably greater than or equal to 130° to less than 180°.

The preform 11 is, during injection moulding, not easily removable from the mould despite the undercut formed by the increase in size of the external diameter, because the preform collar 8 is formed in the jaws of the injection mould, which are opened and closed radially. Owing to the decreasing internal diameter of the preform collar 8 and the body portion 2, the injection core can also easily be removed from the mould axially. Finally, the body portion 2, with the end portion 3 of the preform 11, can also easily be removed from the mould axially owing to the external diameter decreasing toward the end portion 3.

As may be seen from FIG. 2, the wall thickness w of the body portion 2 increases constantly despite the external diameter a decreasing along its longitudinal extension. In this case, the wall thickness w of the body portion 2 does not exceed a maximum wall thickness of 6 mm.

At the transition from the body portion 2 to the dome-shaped end portion 3, a sudden change in wall thickness is avoided. For this purpose, the dome-shaped end portion has a wall thickness t which is reduced from the maximum wall thickness w of the body portion 2 up to an injection point 9 by 0% to 50%. The wall thickness in the injection point 9 is in this case not taken into account. The wall thickness t in the end portion 3 is in this case selected depending on the type of bottom to be manufactured, in order to impart optimum rigidity and stability to the fully blow-moulded container.

A further variant embodiment, illustrated in FIG. 3, of a preform according to the invention is denoted overall by reference numeral 21. Again, like parts are denoted by the same reference numerals as in the preceding figures. The body portion 2 of the preform 21 has, again, a wall thickness w which is reduced from the preform collar 8 to the end portion 3. The wall thickness of the end portion 3 is denoted, again, by reference symbol t; the injection point is denoted by 9. The preform collar 8 has an external diameter d which decreases in size over the longitudinal extension of the preform collar 8 toward the body portion 2. FIG. 3 shows that an inner wall 81 of the preform collar 8 merges with the inner wall 21 of the body portion 2 of the preform 1 at an obtuse angle α. The angle of merging α is preferably 130° to less than 180°. This measure substantially prevents sudden transitions.

The preform which is illustrated in FIG. 4 and denoted in its entirety by reference numeral 31 is embodied for example for the manufacture of a wide-necked vessel. The neck portion 4 has an opening 5, the opening diameter of which is larger than the external diameter a of the body portion 2. Accordingly, the preform collar also has an external diameter d which is reduced from the much larger external diameter of the neck portion 4 toward the body portion 2. The external diameter a of the body portion 2 of the preform 1 decreases toward the end portion 3 now only slightly. Despite the relatively large difference in the external diameter of the preform collar 8 below the transport ring 7 and of the body portion 2 adjoining the preform collar 8, the outer wall 82 of the preform collar 8 and the outer wall 22 of the body portion 2 enclose at their mutual transition an obtuse angle β of from preferably 130° to less than 180°.

A common feature of the illustrated preforms is the fact that the wall thickness w of the body portion 2 is reduced or increases in size over its longitudinal extension from the transition to the preform collar 8 up to the transition to the dome-shaped end portion 3 substantially constantly by up to 2 mm. The internal diameter i and the external diameter a of the body portion 2 are reduced in this case from the preform collar 8 up to the dome-shaped end portion 3 substantially constantly by 0.1-3.5 mm.

The preform embodied in accordance with the invention does not display any sudden, staggered changes in wall thickness. As a result, during manufacture thereof by plastics material injection moulding, local exposure to heat can be avoided, and fluctuations in wall thickness over the circumference are prevented. The embodiment of the preform allows the desired distribution of material on the preform that is required for the required strength and heat resistance of the plastics material bottle stretch blow-moulded therefrom, without more material having to be provided at the injection point. The invention can be applied to all plastics materials which are suitable for the injection blow moulding or injection stretch blow moulding method. Advantageously, at least 85% of the body portion of the preform is made of materials selected from the group consisting of polyesters (including PET, PBT, PLA, and PEN), copolyesters, polyolefins (in particular PP, HDPE) and polystyrenes (GPS or HIPS).

The preform according to the invention is optimised for manufacture by injection moulding, extrusion or spray foaming and serves as an intermediate product for the manufacture of plastics material bottles or wide-necked vessels in an injection blow moulding or injection stretch blow moulding method. 

1. A preform for manufacturing plastics material bottles or wide-necked vessels, comprising: a rigid, substantially elongate, frustoconical body portion that is closed at one of its longitudinal ends by a dome-shaped end portion and at its opposite longitudinal end adjoins, via a preform collar, a neck portion provided with a pouring opening and has an external diameter which is reduced from the preform collar to the end portion; the body portion having a wall thickness that changes over its longitudinal extension substantially constantly by up to ±2 mm, and has an internal diameter that decreases substantially constantly from a transition to the preform collar up to a transition to the dome-shaped end portion.
 2. The preform according to claim 1, wherein the preform collar has an external diameter that changes from the neck portion to the body portion, while its internal diameter decreases substantially constantly from the neck portion to the body portion.
 3. The preform according to claim 2, wherein the external diameter of the preform collar increases in size from the neck portion to the body portion at least in a portion thereof.
 4. The preform according to claim 2, wherein the external diameter of the preform collar decreases in size from the neck portion to the body portion at least in a portion thereof.
 5. The preform according to claim 1, wherein an inner wall and an outer wall of the preform collar join with an adjoining inner wall or outer wall of the body portion at obtuse angles that are from about 130° to less than 180°.
 6. The preform according to claim 1, wherein the body portion has a minimum wall thickness greater than 0.8 mm.
 7. The preform according to claim 1, wherein the body portion does not exceed a maximum wall thickness of 6 mm.
 8. The preform according to claim 1, wherein the internal diameter of the body portion is reduced from the preform collar to the dome-shaped end portion by 0.1 mm-3.5 mm.
 9. The preform according to claim 1, wherein the body portion has an external diameter which is reduced from the preform collar to the dome-shaped end portion by 0.1-3.5 mm.
 10. The preform according to claim 1, wherein the dome-shaped end portion has a wall thickness that is reduced from the wall thickness of the body portion up to an injection point by 0% to 50%, and wherein the wall thickness is not taken into account in the injection point.
 11. The preform according to claim 1, wherein at least 85% of the body portion of the preform is made of materials selected from the group comprising, polyesters, including PET, PBT, PLA, and PEN, copolyesters, polyolefins, PP, HDPE, and polystyrenes, including GPS or HIPS.
 12. The preform according to claim 1, wherein the perform is manufactured by injection moulding, extrusion or spray foaming.
 13. The preform according to claim 1 wherein the preform collar is separated from the neck portion by a transport ring.
 14. The preform according claim 1, wherein the wall thickness of the preform collar increases constantly over at least a partial region.
 15. The perform of claim 1, wherein the perform forms a plastics material bottle by an injection blow moulding or injection stretch blow moulding process. 